如果我知道一个字段的值，如何获取FireStore文档的ID？(在Swift)

import Firebase
import FirebaseFirestore

let db = Firestore.firestore()

let query = db.collection("collectionName").whereField("fieldName", isEqualTo: "fieldValue")

query.getDocuments { (snapshot, error) in
    if let error = error {
        print("Error getting documents: \(error)")
    } else {
        for document in snapshot!.documents {
            let documentID = document.documentID
            print("Document ID: \(documentID)")
        }
    }
}